An active neurotoxic metabolite of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine. The compound reduces dopamine levels, inhibits the biosynthesis of catecholamines, depletes cardiac norepinephrine and inactivates tyrosine hydroxylase. These and other toxic effects lead to cessation of oxidative phosphorylation, ATP depletion, and cell death. The compound, which is related to paraquat, has also been used as an herbicide.